This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. INTRODUCTION One of the most fundamental aspects of human cognition is our ability to recognize familiar objects regardless of the particular viewing conditions. For example, one can recognize an object as a coffee cup nearly instantaneously and with little perceived effort whether it is very close and takes up much of our visual field, or far away and takes up very little of our visual field. However, the manner by which the brain represents and processes visual objects to afford such invariant object perception is not understood. In this study, we examined how invariance to object size develops across visual cortex, and whether the sensitivity to object size is a static or dynamic property of a visual area. MATERIALS AND METHODS We examined the representations underlying invariant object recognition using functional magnetic resonance imaging techniques in a 3.0 Tesla GE scanner. First, the boundaries of early retinotopic areas were defined using standard techniques. Next, object-selective areas were defined as those regions that responded higher to intact images of objects compared to scrambled versions of those objects. All analyses were performed on regions selected using these analyses. Eight participants completed in ten runs in which they viewed centrally-presented line drawings of animals and cars in four sizes, extending into 3 , 6 , 9 , and 12 of eccentricity. In addition, participants were presented new objects from the same categories, scrambled images, and fixation-only trials that served as baseline. Participants performed two tasks while viewing the images that directed their attention to certain aspects of the stimuli. During the Size Task, participants categorized each image as small, medium, or large. During the Object Task, participants categorized each image as an animal, vehicle, or neither (scrambled and fixation-only). CONCLUSION Size invariance develops incrementally across the hierarchy of visual areas, but even high-level visual areas retain some degree of size-preference. Furthermore, size invariance is not a static property of a visual area, but can be modulated by task demands, becoming more or less invariant as needed.
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